Over the past several years, multiple test devices on microscope slides, or more generally on a level support, have been developed, comprising a series of aligned deposits which are the supports of a biochemical reaction when contacted with a biological sample. After an eventual reaction with fluorescent revealing reagents, the device is read, that is to say, the reaction on each spot is quantified.
The slides may be made of glass or transparent plastic material. The number of spots on a slide can range from a few units to several thousand. The diameter of the spots is generally comprised between 50 and 250 microns. Said deposits are generally referred to as microarrays, an American term which has come into international usage.
According to a first variant, the deposits are constituted of nucleic acid sequences (DNA, deoxyribonucleic acid) and the biological sample to be tested contains a mixture of nucleic acid sequences, for example the amplified forms of its messenger RNA (ribonucleic acid) called complementary DNA (cDNA). Each deposit hybridizes with its corresponding cDNA. The hybridization reaction can be visualized and quantified by fluorescence, either by labelling the cDNA itself, or by labelling the areas of hybridization with a specific dye.
In a second variant (such as for example serological tests), the biological sample to be tested contains serum or plasma, and reacts with a slide carrying reactive elements, for example proteins, cells, subcellular fractions, bacteria, viruses, etc., placed in advance on the slide. After this first reaction, the slide is placed in contact with a revealing agent.
In all cases, it is necessary to carry out an operation whereby the signal specific to each spot is read. Said signal can be a radioisotope, a color reaction resulting from an enzymatic amplification, or else a fluorescence signal. It is in the latter case where it becomes possible to attain the resolution required by the increasing density of spots.
Whereas spotting methods have been perfected and the usefulness of multiple determinations has been confirmed, with several possible applications in the diagnostics field, there is no fluorescence reader having the required performance available at an acceptable cost to a clinical laboratory. It is in this latter category that the invention is positioned.
Currently available apparatuses make use of a laser scan to probe the slide. In general, three different lasers are necessary to acquire the different signals emitted by the spots. The image is then reconstituted on a screen and the operator visually moves a grid frame, while trying to align the mesh of the grid with the images of the spots. This operation is far from being entirely satisfactory because the spots are irregular. Of course such apparatuses are very expensive, on the order of US$ 100,000. They are designed for research purposes to process a small number of slides bearing a very large number of spots and are not adapted to the routine operations of a clinical laboratory, which processes many slides bearing a small number of spots.
There is therefore a real need for analytical microarray slide readers which enable rapid, reliable and automated analysis. In the field of serology there is in particular an unsatisfied need for a random access slide reader, which can process a slide in a short period of time (typically a few seconds) and respond to urgent diagnosis in the case of infectious diseases. The invention offers a solution to these needs.